title: A study of the kinetics of La3+-promoted methanolysis of S-aryl methylphosphonothioates: possible methodology for decontamination of EA 2192, the toxic byproduct of VX hydrolysis.
abstract: The kinetics of the La3+-catalyzed methanolysis of a series of S-aryl methylphosphonothioates (4a-e, phenyl substituents = 3,5-dichloro, 4-chloro, 4-fluoro, 4-H, 4-methoxy) were studied at 25 °C with s(s)pH control. The reaction involves saturation binding of the anionic substrates to dimeric La3+/methoxide catalysts formulated as La2(3+)(-OCH3)x, where x = 2-5 depending on the solution s(s)pH. Cleavage of the La3+-bound methylphosphonothioates is fast, ranging from 5 × 10(-3) s(-1) to 5.5 × 10-(5) s(-1) for substrates 4a-e at a s(s)pH of 8.4 and 1.6 × 10(-1) s(-1) to 4 × 10(-3) s(-1) at a s(s)pH of 11.7. The rate accelerations for the methanolysis of substrates 4a-e, relative to their background methoxide-promoted reactions, average 7 × 10(10) and 1.5 × 10(9), respectively, at s(s)pH's of 8.4 and 11.7. The catalytic system is predicted to cleave EA 2192 (S-2(N,N-di-iso-propylaminoethyl)methylphosphonothioate), a toxic byproduct of the hydrolysis of VX, with a t1/2 between 4 and 8 min at a s(s)pH of 8.4, and 27 min at a s(s)pH of 11.7.
authors.affiliation: Department of Chemistry, Queen's University Kingston, Ontario, Canada.
authors.forename: Basab B
authors.initials: BB
authors.lastname: Dhar
authors.forename: David R
authors.initials: DR
authors.lastname: Edwards
authors.forename: R Stan
authors.initials: RS
authors.lastname: Brown
mesh_terms: D006868:Hydrolysis; D007700:Kinetics; D007811:Lanthanum / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D009946:Organothiophosphorus Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D009946:Organothiophosphorus Compounds; D013438:Sulfhydryl Compounds; D007811:Lanthanum